This invention is directed to a soldering method by which metals can be joined for electrical and mechanical purposes. This soldering method includes the use of a lead-cadmium-zinc solder.
Conventional tin-lead solder has been almost exclusively used in the electronics industry for many years. In spite of its many advantages and universal usage, it has some significant disadvantages. In addition to its high cost, which has been rapidly increasing in the past few years, it has limited resistance to thermal fatigue. Many instances of solder joint cracking have been observed. While some of these instances may be attributed to design deficiencies, it would be advantageous to have a solder which is more resistant to thermal fatigue. Furthermore, recent developments in polyimide materials have made it possible to extend the upper temperature limit of printed wiring boards beyond the range of eutectic tin-lead solder. Presently, polyimide printed wiring boards are only used for their manufacturing advantages including having less tendency to smear during drilling and less tendency to craze during rework, but their high temperature capability may be employed in the future. The use of the present lead-cadmium-zinc solder of this invention is compatible with polyimide printed wiring boards including its higher temperature capability and provides economy and reliability on boards of all materials.